Export of internal Abseil changes

--
03700706d80f0939e2b5b8c02a326f045b643730 by Abseil Team <absl-team@google.com>:

Reduced latency and code-size of some InlinedVector methods:

1. Simpler fast path for push_back/emplace_back.
2. Do not inline slow path of push-back/emplace_back.
3. Simplify resize implementation.

Performance:
A simple benchmark that does the following per iteration:

```
push_back on an InlinedVector<int64>
push_back on an InlinedVector<bool>
```

Sees iteration time go from 4.3ns to 2.8ns and code size shrink from 1129 bytes to 175 bytes.

PiperOrigin-RevId: 343335635

--
16f74277a9e8bf228c164b053da8b8098f76de62 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 343332753

--
886b6d5d0244783d309e34f03c21710f411e3cb3 by Abseil Team <absl-team@google.com>:

Optimize `Status::Status`: When creating a status, we currently create an empty struct first, then assign fields. This is suboptimal: https://screenshot.googleplex.com/5HqDuFBKUEqrVgy.

Relevant Benchmarks:
```
BM_StatusCopyError_Deep/threads:1              26.9ns ±13%   21.2ns ±16%  -21.46%  (p=0.000 n=15+15)
BM_StatusCopyError_Deep/threads:2              32.0ns ±30%   25.6ns ±37%  -20.17%  (p=0.004 n=15+14)
BM_StatusCopyError_Deep/threads:4              37.4ns ±84%   30.6ns ±58%  -18.26%  (p=0.029 n=15+15)
BM_StatusCopyError_Deep/threads:8              47.2ns ±33%   33.5ns ±56%  -28.91%  (p=0.000 n=15+14)
```

PiperOrigin-RevId: 343303312

--
2f9d945654292e8e52cad410fa41dae794cff42c by Abseil Team <absl-team@google.com>:

Set SOVERSION for the installed libraries

PiperOrigin-RevId: 343287682

--
600bbfffe91cfbdc60b43cdad5619258298d0b0d by Abseil Team <absl-team@google.com>:

Fix a typo in a comment (than -> that)

PiperOrigin-RevId: 343187724

--
310c82cd97b3f1f0d1ee93a0ee2b0aee828b2a93 by Abseil Team <absl-team@google.com>:

Simplify unaligned memory access functions.

The #ifdef to produce calls to __sanitizer_unaligned_load16 etc were needed in past versions of this code, when we were lying to the compiler about the alignment of the loads/stores, by using a reinterpret_cast.

However, a year ago, absl switched to simply use memcpy. Sanitizers support this correctly by default, nothing extra is required.

PiperOrigin-RevId: 343159883

--
bdf6fcf99180c371fda6ba8af82fd44656e372fa by Gennadiy Rozental <rogeeff@google.com>:

Migrate usage flags to global variables instead of modeling them as Abseil Flags.

Also introduce new semantic for --help=substring command line argument.

PiperOrigin-RevId: 343019883
GitOrigin-RevId: 03700706d80f0939e2b5b8c02a326f045b643730
Change-Id: I4ad40dfa9606f8b8bfb2d91fd09e327105311bfb

14 files changed, 449 insertions, 235 deletions

diff --git a/CMake/AbseilHelpers.cmake b/CMake/AbseilHelpers.cmake
index e85deba8..e88507de 100644
--- a/CMake/AbseilHelpers.cmake
+++ b/CMake/AbseilHelpers.cmake
@@ -260,6 +260,8 @@ Cflags: -I\${includedir}${PC_CFLAGS}\n")
     if(ABSL_ENABLE_INSTALL)
       set_target_properties(${_NAME} PROPERTIES
         OUTPUT_NAME "absl_${_NAME}"
+        # TODO(b/173696973): Figure out how to set SOVERSION for LTS releases.
+        SOVERSION 0
       )
     endif()
   else()
diff --git a/absl/base/internal/unaligned_access.h b/absl/base/internal/unaligned_access.h
index 080c197c..093dd9b4 100644
--- a/absl/base/internal/unaligned_access.h
+++ b/absl/base/internal/unaligned_access.h
@@ -31,70 +31,6 @@
 // The unaligned API is C++ only.  The declarations use C++ features
 // (namespaces, inline) which are absent or incompatible in C.
 #if defined(__cplusplus)
-
-#if defined(ABSL_HAVE_ADDRESS_SANITIZER) || \
-    defined(ABSL_HAVE_THREAD_SANITIZER) || defined(ABSL_HAVE_MEMORY_SANITIZER)
-// Consider we have an unaligned load/store of 4 bytes from address 0x...05.
-// AddressSanitizer will treat it as a 3-byte access to the range 05:07 and
-// will miss a bug if 08 is the first unaddressable byte.
-// ThreadSanitizer will also treat this as a 3-byte access to 05:07 and will
-// miss a race between this access and some other accesses to 08.
-// MemorySanitizer will correctly propagate the shadow on unaligned stores
-// and correctly report bugs on unaligned loads, but it may not properly
-// update and report the origin of the uninitialized memory.
-// For all three tools, replacing an unaligned access with a tool-specific
-// callback solves the problem.
-
-#include <sanitizer/common_interface_defs.h>
-
-namespace absl {
-ABSL_NAMESPACE_BEGIN
-namespace base_internal {
-
-inline uint16_t UnalignedLoad16(const void *p) {
-  return __sanitizer_unaligned_load16(p);
-}
-
-inline uint32_t UnalignedLoad32(const void *p) {
-  return __sanitizer_unaligned_load32(p);
-}
-
-inline uint64_t UnalignedLoad64(const void *p) {
-  return __sanitizer_unaligned_load64(p);
-}
-
-inline void UnalignedStore16(void *p, uint16_t v) {
-  __sanitizer_unaligned_store16(p, v);
-}
-
-inline void UnalignedStore32(void *p, uint32_t v) {
-  __sanitizer_unaligned_store32(p, v);
-}
-
-inline void UnalignedStore64(void *p, uint64_t v) {
-  __sanitizer_unaligned_store64(p, v);
-}
-
-}  // namespace base_internal
-ABSL_NAMESPACE_END
-}  // namespace absl
-
-#define ABSL_INTERNAL_UNALIGNED_LOAD16(_p) \
-  (absl::base_internal::UnalignedLoad16(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD32(_p) \
-  (absl::base_internal::UnalignedLoad32(_p))
-#define ABSL_INTERNAL_UNALIGNED_LOAD64(_p) \
-  (absl::base_internal::UnalignedLoad64(_p))
-
-#define ABSL_INTERNAL_UNALIGNED_STORE16(_p, _val) \
-  (absl::base_internal::UnalignedStore16(_p, _val))
-#define ABSL_INTERNAL_UNALIGNED_STORE32(_p, _val) \
-  (absl::base_internal::UnalignedStore32(_p, _val))
-#define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
-  (absl::base_internal::UnalignedStore64(_p, _val))
-
-#else
-
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
@@ -141,8 +77,6 @@ ABSL_NAMESPACE_END
 #define ABSL_INTERNAL_UNALIGNED_STORE64(_p, _val) \
   (absl::base_internal::UnalignedStore64(_p, _val))
 
-#endif
-
 #endif  // defined(__cplusplus), end of unaligned API
 
 #endif  // ABSL_BASE_INTERNAL_UNALIGNED_ACCESS_H_
diff --git a/absl/base/optimization.h b/absl/base/optimization.h
index 2e31376c..393fc3a4 100644
--- a/absl/base/optimization.h
+++ b/absl/base/optimization.h
@@ -179,7 +179,7 @@
 #endif
 
 // ABSL_INTERNAL_ASSUME(cond)
-// Informs the compiler than a condition is always true and that it can assume
+// Informs the compiler that a condition is always true and that it can assume
 // it to be true for optimization purposes. The call has undefined behavior if
 // the condition is false.
 // In !NDEBUG mode, the condition is checked with an assert().
diff --git a/absl/container/internal/inlined_vector.h b/absl/container/internal/inlined_vector.h
index 4d80b727..c98c25c4 100644
--- a/absl/container/internal/inlined_vector.h
+++ b/absl/container/internal/inlined_vector.h
@@ -462,6 +462,9 @@ class Storage {
     Inlined inlined;
   };
 
+  template <typename... Args>
+  ABSL_ATTRIBUTE_NOINLINE reference EmplaceBackSlow(Args&&... args);
+
   Metadata metadata_;
   Data data_;
 };
@@ -542,48 +545,42 @@ template <typename T, size_t N, typename A>
 template <typename ValueAdapter>
 auto Storage<T, N, A>::Resize(ValueAdapter values, size_type new_size) -> void {
   StorageView storage_view = MakeStorageView();
-
-  IteratorValueAdapter<MoveIterator> move_values(
-      MoveIterator(storage_view.data));
-
-  AllocationTransaction allocation_tx(GetAllocPtr());
-  ConstructionTransaction construction_tx(GetAllocPtr());
-
-  absl::Span<value_type> construct_loop;
-  absl::Span<value_type> move_construct_loop;
-  absl::Span<value_type> destroy_loop;
-
-  if (new_size > storage_view.capacity) {
+  auto* const base = storage_view.data;
+  const size_type size = storage_view.size;
+  auto* alloc = GetAllocPtr();
+  if (new_size <= size) {
+    // Destroy extra old elements.
+    inlined_vector_internal::DestroyElements(alloc, base + new_size,
+                                             size - new_size);
+  } else if (new_size <= storage_view.capacity) {
+    // Construct new elements in place.
+    inlined_vector_internal::ConstructElements(alloc, base + size, &values,
+                                               new_size - size);
+  } else {
+    // Steps:
+    //  a. Allocate new backing store.
+    //  b. Construct new elements in new backing store.
+    //  c. Move existing elements from old backing store to now.
+    //  d. Destroy all elements in old backing store.
+    // Use transactional wrappers for the first two steps so we can roll
+    // back if necessary due to exceptions.
+    AllocationTransaction allocation_tx(alloc);
     size_type new_capacity = ComputeCapacity(storage_view.capacity, new_size);
     pointer new_data = allocation_tx.Allocate(new_capacity);
-    construct_loop = {new_data + storage_view.size,
-                      new_size - storage_view.size};
-    move_construct_loop = {new_data, storage_view.size};
-    destroy_loop = {storage_view.data, storage_view.size};
-  } else if (new_size > storage_view.size) {
-    construct_loop = {storage_view.data + storage_view.size,
-                      new_size - storage_view.size};
-  } else {
-    destroy_loop = {storage_view.data + new_size, storage_view.size - new_size};
-  }
-
-  construction_tx.Construct(construct_loop.data(), &values,
-                            construct_loop.size());
 
-  inlined_vector_internal::ConstructElements(
-      GetAllocPtr(), move_construct_loop.data(), &move_values,
-      move_construct_loop.size());
+    ConstructionTransaction construction_tx(alloc);
+    construction_tx.Construct(new_data + size, &values, new_size - size);
 
-  inlined_vector_internal::DestroyElements(GetAllocPtr(), destroy_loop.data(),
-                                           destroy_loop.size());
+    IteratorValueAdapter<MoveIterator> move_values((MoveIterator(base)));
+    inlined_vector_internal::ConstructElements(alloc, new_data, &move_values,
+                                               size);
 
-  construction_tx.Commit();
-  if (allocation_tx.DidAllocate()) {
+    inlined_vector_internal::DestroyElements(alloc, base, size);
+    construction_tx.Commit();
     DeallocateIfAllocated();
     AcquireAllocatedData(&allocation_tx);
     SetIsAllocated();
   }
-
   SetSize(new_size);
 }
 
@@ -684,44 +681,50 @@ template <typename T, size_t N, typename A>
 template <typename... Args>
 auto Storage<T, N, A>::EmplaceBack(Args&&... args) -> reference {
   StorageView storage_view = MakeStorageView();
+  const auto n = storage_view.size;
+  if (ABSL_PREDICT_TRUE(n != storage_view.capacity)) {
+    // Fast path; new element fits.
+    pointer last_ptr = storage_view.data + n;
+    AllocatorTraits::construct(*GetAllocPtr(), last_ptr,
+                               std::forward<Args>(args)...);
+    AddSize(1);
+    return *last_ptr;
+  }
+  // TODO(b/173712035): Annotate with musttail attribute to prevent regression.
+  return EmplaceBackSlow(std::forward<Args>(args)...);
+}
 
+template <typename T, size_t N, typename A>
+template <typename... Args>
+auto Storage<T, N, A>::EmplaceBackSlow(Args&&... args) -> reference {
+  StorageView storage_view = MakeStorageView();
   AllocationTransaction allocation_tx(GetAllocPtr());
-
   IteratorValueAdapter<MoveIterator> move_values(
       MoveIterator(storage_view.data));
-
-  pointer construct_data;
-  if (storage_view.size == storage_view.capacity) {
-    size_type new_capacity = NextCapacity(storage_view.capacity);
-    construct_data = allocation_tx.Allocate(new_capacity);
-  } else {
-    construct_data = storage_view.data;
-  }
-
+  size_type new_capacity = NextCapacity(storage_view.capacity);
+  pointer construct_data = allocation_tx.Allocate(new_capacity);
   pointer last_ptr = construct_data + storage_view.size;
 
+  // Construct new element.
   AllocatorTraits::construct(*GetAllocPtr(), last_ptr,
                              std::forward<Args>(args)...);
-
-  if (allocation_tx.DidAllocate()) {
-    ABSL_INTERNAL_TRY {
-      inlined_vector_internal::ConstructElements(
-          GetAllocPtr(), allocation_tx.GetData(), &move_values,
-          storage_view.size);
-    }
-    ABSL_INTERNAL_CATCH_ANY {
-      AllocatorTraits::destroy(*GetAllocPtr(), last_ptr);
-      ABSL_INTERNAL_RETHROW;
-    }
-
-    inlined_vector_internal::DestroyElements(GetAllocPtr(), storage_view.data,
-                                             storage_view.size);
-
-    DeallocateIfAllocated();
-    AcquireAllocatedData(&allocation_tx);
-    SetIsAllocated();
+  // Move elements from old backing store to new backing store.
+  ABSL_INTERNAL_TRY {
+    inlined_vector_internal::ConstructElements(
+        GetAllocPtr(), allocation_tx.GetData(), &move_values,
+        storage_view.size);
   }
+  ABSL_INTERNAL_CATCH_ANY {
+    AllocatorTraits::destroy(*GetAllocPtr(), last_ptr);
+    ABSL_INTERNAL_RETHROW;
+  }
+  // Destroy elements in old backing store.
+  inlined_vector_internal::DestroyElements(GetAllocPtr(), storage_view.data,
+                                           storage_view.size);
 
+  DeallocateIfAllocated();
+  AcquireAllocatedData(&allocation_tx);
+  SetIsAllocated();
   AddSize(1);
   return *last_ptr;
 }
diff --git a/absl/flags/BUILD.bazel b/absl/flags/BUILD.bazel
index 2bd94780..78d6da74 100644
--- a/absl/flags/BUILD.bazel
+++ b/absl/flags/BUILD.bazel
@@ -416,6 +416,7 @@ cc_test(
         ":flag",
         ":parse",
         ":reflection",
+        ":usage_internal",
         "//absl/base:raw_logging_internal",
         "//absl/base:scoped_set_env",
         "//absl/strings",
diff --git a/absl/flags/CMakeLists.txt b/absl/flags/CMakeLists.txt
index 88551914..e5083d7b 100644
--- a/absl/flags/CMakeLists.txt
+++ b/absl/flags/CMakeLists.txt
@@ -366,6 +366,7 @@ absl_cc_test(
     absl::flags
     absl::flags_parse
     absl::flags_reflection
+    absl::flags_usage_internal
     absl::raw_logging_internal
     absl::scoped_set_env
     absl::span
diff --git a/absl/flags/internal/usage.cc b/absl/flags/internal/usage.cc
index 75573227..f29d7c9b 100644
--- a/absl/flags/internal/usage.cc
+++ b/absl/flags/internal/usage.cc
@@ -37,26 +37,26 @@
 #include "absl/strings/str_split.h"
 #include "absl/strings/string_view.h"
 
-ABSL_FLAG(bool, help, false,
-          "show help on important flags for this binary [tip: all flags can "
-          "have two dashes]");
-ABSL_FLAG(bool, helpfull, false, "show help on all flags");
-ABSL_FLAG(bool, helpshort, false,
-          "show help on only the main module for this program");
-ABSL_FLAG(bool, helppackage, false,
-          "show help on all modules in the main package");
-ABSL_FLAG(bool, version, false, "show version and build info and exit");
-ABSL_FLAG(bool, only_check_args, false, "exit after checking all flags");
-ABSL_FLAG(std::string, helpon, "",
-          "show help on the modules named by this flag value");
-ABSL_FLAG(std::string, helpmatch, "",
-          "show help on modules whose name contains the specified substr");
+// Dummy global variables to prevent anyone else defining these.
+bool FLAGS_help = false;
+bool FLAGS_helpfull = false;
+bool FLAGS_helpshort = false;
+bool FLAGS_helppackage = false;
+bool FLAGS_version = false;
+bool FLAGS_only_check_args = false;
+bool FLAGS_helpon = false;
+bool FLAGS_helpmatch = false;
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace flags_internal {
 namespace {
 
+using PerFlagFilter = std::function<bool(const absl::CommandLineFlag&)>;
+
+// Maximum length size in a human readable format.
+constexpr size_t kHrfMaxLineLength = 80;
+
 // This class is used to emit an XML element with `tag` and `text`.
 // It adds opening and closing tags and escapes special characters in the text.
 // For example:
@@ -109,9 +109,12 @@ class FlagHelpPrettyPrinter {
  public:
   // Pretty printer holds on to the std::ostream& reference to direct an output
   // to that stream.
-  FlagHelpPrettyPrinter(int max_line_len, std::ostream& out)
+  FlagHelpPrettyPrinter(size_t max_line_len, size_t min_line_len,
+                        size_t wrapped_line_indent, std::ostream& out)
       : out_(out),
         max_line_len_(max_line_len),
+        min_line_len_(min_line_len),
+        wrapped_line_indent_(wrapped_line_indent),
         line_len_(0),
         first_line_(true) {}
 
@@ -165,13 +168,12 @@ class FlagHelpPrettyPrinter {
 
   void StartLine() {
     if (first_line_) {
-      out_ << "    ";
-      line_len_ = 4;
+      line_len_ = min_line_len_;
       first_line_ = false;
     } else {
-      out_ << "      ";
-      line_len_ = 6;
+      line_len_ = min_line_len_ + wrapped_line_indent_;
     }
+    out_ << std::string(line_len_, ' ');
   }
   void EndLine() {
     out_ << '\n';
@@ -180,13 +182,15 @@ class FlagHelpPrettyPrinter {
 
  private:
   std::ostream& out_;
-  const int max_line_len_;
-  int line_len_;
+  const size_t max_line_len_;
+  const size_t min_line_len_;
+  const size_t wrapped_line_indent_;
+  size_t line_len_;
   bool first_line_;
 };
 
 void FlagHelpHumanReadable(const CommandLineFlag& flag, std::ostream& out) {
-  FlagHelpPrettyPrinter printer(80, out);  // Max line length is 80.
+  FlagHelpPrettyPrinter printer(kHrfMaxLineLength, 4, 2, out);
 
   // Flag name.
   printer.Write(absl::StrCat("--", flag.Name()));
@@ -222,7 +226,7 @@ void FlagHelpHumanReadable(const CommandLineFlag& flag, std::ostream& out) {
 // If a flag's help message has been stripped (e.g. by adding '#define
 // STRIP_FLAG_HELP 1' then this flag will not be displayed by '--help'
 // and its variants.
-void FlagsHelpImpl(std::ostream& out, flags_internal::FlagKindFilter filter_cb,
+void FlagsHelpImpl(std::ostream& out, PerFlagFilter filter_cb,
                    HelpFormat format, absl::string_view program_usage_message) {
   if (format == HelpFormat::kHumanReadable) {
     out << flags_internal::ShortProgramInvocationName() << ": "
@@ -257,10 +261,10 @@ void FlagsHelpImpl(std::ostream& out, flags_internal::FlagKindFilter filter_cb,
     // If the flag has been stripped, pretend that it doesn't exist.
     if (flag.Help() == flags_internal::kStrippedFlagHelp) return;
 
-    std::string flag_filename = flag.Filename();
-
     // Make sure flag satisfies the filter
-    if (!filter_cb || !filter_cb(flag_filename)) return;
+    if (!filter_cb(flag)) return;
+
+    std::string flag_filename = flag.Filename();
 
     matching_flags[std::string(flags_internal::Package(flag_filename))]
                   [flag_filename]
@@ -290,15 +294,34 @@ void FlagsHelpImpl(std::ostream& out, flags_internal::FlagKindFilter filter_cb,
   }
 
   if (format == HelpFormat::kHumanReadable) {
+    FlagHelpPrettyPrinter printer(kHrfMaxLineLength, 0, 0, out);
+
     if (filter_cb && matching_flags.empty()) {
-      out << "  No modules matched: use -helpfull\n";
+      printer.Write("No flags matched.\n", true);
     }
+    printer.EndLine();
+    printer.Write(
+        "Try --helpfull to get a list of all flags or --help=substring "
+        "shows help for flags which include specified substring in either "
+        "in the name, or description or path.\n",
+        true);
   } else {
     // The end of the document.
     out << "</AllFlags>\n";
   }
 }
 
+void FlagsHelpImpl(std::ostream& out,
+                   flags_internal::FlagKindFilter filename_filter_cb,
+                   HelpFormat format, absl::string_view program_usage_message) {
+  FlagsHelpImpl(
+      out,
+      [&](const absl::CommandLineFlag& flag) {
+        return filename_filter_cb && filename_filter_cb(flag.Filename());
+      },
+      format, program_usage_message);
+}
+
 }  // namespace
 
 // --------------------------------------------------------------------
@@ -310,7 +333,7 @@ void FlagHelp(std::ostream& out, const CommandLineFlag& flag,
 }
 
 // --------------------------------------------------------------------
-// Produces the help messages for all flags matching the filter.
+// Produces the help messages for all flags matching the filename filter.
 // If filter is empty produces help messages for all flags.
 void FlagsHelp(std::ostream& out, absl::string_view filter, HelpFormat format,
                absl::string_view program_usage_message) {
@@ -325,66 +348,175 @@ void FlagsHelp(std::ostream& out, absl::string_view filter, HelpFormat format,
 // If so, handles them appropriately.
 int HandleUsageFlags(std::ostream& out,
                      absl::string_view program_usage_message) {
-  if (absl::GetFlag(FLAGS_helpshort)) {
-    flags_internal::FlagsHelpImpl(
-        out, flags_internal::GetUsageConfig().contains_helpshort_flags,
-        HelpFormat::kHumanReadable, program_usage_message);
-    return 1;
-  }
+  switch (GetFlagsHelpMode()) {
+    case HelpMode::kNone:
+      break;
+    case HelpMode::kImportant:
+      flags_internal::FlagsHelpImpl(
+          out, flags_internal::GetUsageConfig().contains_help_flags,
+          GetFlagsHelpFormat(), program_usage_message);
+      return 1;
+
+    case HelpMode::kShort:
+      flags_internal::FlagsHelpImpl(
+          out, flags_internal::GetUsageConfig().contains_helpshort_flags,
+          GetFlagsHelpFormat(), program_usage_message);
+      return 1;
+
+    case HelpMode::kFull:
+      flags_internal::FlagsHelp(out, "", GetFlagsHelpFormat(),
+                                program_usage_message);
+      return 1;
+
+    case HelpMode::kPackage:
+      flags_internal::FlagsHelpImpl(
+          out, flags_internal::GetUsageConfig().contains_helppackage_flags,
+          GetFlagsHelpFormat(), program_usage_message);
+
+      return 1;
+
+    case HelpMode::kMatch: {
+      std::string substr = GetFlagsHelpMatchSubstr();
+      if (substr.empty()) {
+        // show all options
+        flags_internal::FlagsHelp(out, substr, GetFlagsHelpFormat(),
+                                  program_usage_message);
+      } else {
+        auto filter_cb = [&substr](const absl::CommandLineFlag& flag) {
+          if (absl::StrContains(flag.Name(), substr)) return true;
+          if (absl::StrContains(flag.Filename(), substr)) return true;
+          if (absl::StrContains(flag.Help(), substr)) return true;
+
+          return false;
+        };
+        flags_internal::FlagsHelpImpl(
+            out, filter_cb, HelpFormat::kHumanReadable, program_usage_message);
+      }
 
-  if (absl::GetFlag(FLAGS_helpfull)) {
-    // show all options
-    flags_internal::FlagsHelp(out, "", HelpFormat::kHumanReadable,
-                              program_usage_message);
-    return 1;
+      return 1;
+    }
+    case HelpMode::kVersion:
+      if (flags_internal::GetUsageConfig().version_string)
+        out << flags_internal::GetUsageConfig().version_string();
+      // Unlike help, we may be asking for version in a script, so return 0
+      return 0;
+
+    case HelpMode::kOnlyCheckArgs:
+      return 0;
   }
 
-  if (!absl::GetFlag(FLAGS_helpon).empty()) {
-    flags_internal::FlagsHelp(
-        out, absl::StrCat("/", absl::GetFlag(FLAGS_helpon), "."),
-        HelpFormat::kHumanReadable, program_usage_message);
-    return 1;
-  }
+  return -1;
+}
 
-  if (!absl::GetFlag(FLAGS_helpmatch).empty()) {
-    flags_internal::FlagsHelp(out, absl::GetFlag(FLAGS_helpmatch),
-                              HelpFormat::kHumanReadable,
-                              program_usage_message);
-    return 1;
-  }
+// --------------------------------------------------------------------
+// Globals representing usage reporting flags
+
+namespace {
+
+ABSL_CONST_INIT absl::Mutex help_attributes_guard(absl::kConstInit);
+ABSL_CONST_INIT std::string* match_substr
+    ABSL_GUARDED_BY(help_attributes_guard) = nullptr;
+ABSL_CONST_INIT HelpMode help_mode ABSL_GUARDED_BY(help_attributes_guard) =
+    HelpMode::kNone;
+ABSL_CONST_INIT HelpFormat help_format ABSL_GUARDED_BY(help_attributes_guard) =
+    HelpFormat::kHumanReadable;
+
+}  // namespace
 
-  if (absl::GetFlag(FLAGS_help)) {
-    flags_internal::FlagsHelpImpl(
-        out, flags_internal::GetUsageConfig().contains_help_flags,
-        HelpFormat::kHumanReadable, program_usage_message);
+std::string GetFlagsHelpMatchSubstr() {
+  absl::MutexLock l(&help_attributes_guard);
+  if (match_substr == nullptr) return "";
+  return *match_substr;
+}
 
-    out << "\nTry --helpfull to get a list of all flags.\n";
+void SetFlagsHelpMatchSubstr(absl::string_view substr) {
+  absl::MutexLock l(&help_attributes_guard);
+  if (match_substr == nullptr) match_substr = new std::string;
+  match_substr->assign(substr.data(), substr.size());
+}
 
-    return 1;
+HelpMode GetFlagsHelpMode() {
+  absl::MutexLock l(&help_attributes_guard);
+  // Refer to dummy variales to prevent linker dropping them
+  if (FLAGS_help || FLAGS_helpfull || FLAGS_helpshort || FLAGS_helppackage ||
+      FLAGS_version || FLAGS_only_check_args || FLAGS_helpon ||
+      FLAGS_helpmatch) {
+    help_mode = HelpMode::kNone;
   }
+  return help_mode;
+}
+
+void SetFlagsHelpMode(HelpMode mode) {
+  absl::MutexLock l(&help_attributes_guard);
+  help_mode = mode;
+}
 
-  if (absl::GetFlag(FLAGS_helppackage)) {
-    flags_internal::FlagsHelpImpl(
-        out, flags_internal::GetUsageConfig().contains_helppackage_flags,
-        HelpFormat::kHumanReadable, program_usage_message);
+HelpFormat GetFlagsHelpFormat() {
+  absl::MutexLock l(&help_attributes_guard);
+  return help_format;
+}
+
+void SetFlagsHelpFormat(HelpFormat format) {
+  absl::MutexLock l(&help_attributes_guard);
+  help_format = format;
+}
 
-    out << "\nTry --helpfull to get a list of all flags.\n";
+// Deduces usage flags from the input argument in a form --name=value or
+// --name. argument is already split into name and value before we call this
+// function.
+bool DeduceUsageFlags(absl::string_view name, absl::string_view value) {
+  if (absl::ConsumePrefix(&name, "help")) {
+    if (name == "") {
+      if (value.empty()) {
+        SetFlagsHelpMode(HelpMode::kImportant);
+      } else {
+        SetFlagsHelpMode(HelpMode::kMatch);
+        SetFlagsHelpMatchSubstr(value);
+      }
+      return true;
+    }
 
-    return 1;
+    if (name == "match") {
+      SetFlagsHelpMode(HelpMode::kMatch);
+      SetFlagsHelpMatchSubstr(value);
+      return true;
+    }
+
+    if (name == "on") {
+      SetFlagsHelpMode(HelpMode::kMatch);
+      SetFlagsHelpMatchSubstr(absl::StrCat("/", value, "."));
+      return true;
+    }
+
+    if (name == "full") {
+      SetFlagsHelpMode(HelpMode::kFull);
+      return true;
+    }
+
+    if (name == "short") {
+      SetFlagsHelpMode(HelpMode::kShort);
+      return true;
+    }
+
+    if (name == "package") {
+      SetFlagsHelpMode(HelpMode::kPackage);
+      return true;
+    }
+
+    return false;
   }
 
-  if (absl::GetFlag(FLAGS_version)) {
-    if (flags_internal::GetUsageConfig().version_string)
-      out << flags_internal::GetUsageConfig().version_string();
-    // Unlike help, we may be asking for version in a script, so return 0
-    return 0;
+  if (name == "version") {
+    SetFlagsHelpMode(HelpMode::kVersion);
+    return true;
   }
 
-  if (absl::GetFlag(FLAGS_only_check_args)) {
-    return 0;
+  if (name == "only_check_args") {
+    SetFlagsHelpMode(HelpMode::kOnlyCheckArgs);
+    return true;
   }
 
-  return -1;
+  return false;
 }
 
 }  // namespace flags_internal
diff --git a/absl/flags/internal/usage.h b/absl/flags/internal/usage.h
index 619ccceb..c0bcac57 100644
--- a/absl/flags/internal/usage.h
+++ b/absl/flags/internal/usage.h
@@ -66,17 +66,39 @@ void FlagsHelp(std::ostream& out, absl::string_view filter,
 int HandleUsageFlags(std::ostream& out,
                      absl::string_view program_usage_message);
 
+// --------------------------------------------------------------------
+// Globals representing usage reporting flags
+
+enum class HelpMode {
+  kNone,
+  kImportant,
+  kShort,
+  kFull,
+  kPackage,
+  kMatch,
+  kVersion,
+  kOnlyCheckArgs
+};
+
+// Returns substring to filter help output (--help=substr argument)
+std::string GetFlagsHelpMatchSubstr();
+// Returns the requested help mode.
+HelpMode GetFlagsHelpMode();
+// Returns the requested help format.
+HelpFormat GetFlagsHelpFormat();
+
+// These are corresponding setters to the attributes above.
+void SetFlagsHelpMatchSubstr(absl::string_view);
+void SetFlagsHelpMode(HelpMode);
+void SetFlagsHelpFormat(HelpFormat);
+
+// Deduces usage flags from the input argument in a form --name=value or
+// --name. argument is already split into name and value before we call this
+// function.
+bool DeduceUsageFlags(absl::string_view name, absl::string_view value);
+
 }  // namespace flags_internal
 ABSL_NAMESPACE_END
 }  // namespace absl
 
-ABSL_DECLARE_FLAG(bool, help);
-ABSL_DECLARE_FLAG(bool, helpfull);
-ABSL_DECLARE_FLAG(bool, helpshort);
-ABSL_DECLARE_FLAG(bool, helppackage);
-ABSL_DECLARE_FLAG(bool, version);
-ABSL_DECLARE_FLAG(bool, only_check_args);
-ABSL_DECLARE_FLAG(std::string, helpon);
-ABSL_DECLARE_FLAG(std::string, helpmatch);
-
 #endif  // ABSL_FLAGS_INTERNAL_USAGE_H_
diff --git a/absl/flags/internal/usage_test.cc b/absl/flags/internal/usage_test.cc
index 6e583fbe..b5c2487d 100644
--- a/absl/flags/internal/usage_test.cc
+++ b/absl/flags/internal/usage_test.cc
@@ -87,6 +87,11 @@ class UsageReportingTest : public testing::Test {
     default_config.normalize_filename = &NormalizeFileName;
     absl::SetFlagsUsageConfig(default_config);
   }
+  ~UsageReportingTest() override {
+    flags::SetFlagsHelpMode(flags::HelpMode::kNone);
+    flags::SetFlagsHelpMatchSubstr("");
+    flags::SetFlagsHelpFormat(flags::HelpFormat::kHumanReadable);
+  }
 
  private:
   absl::FlagSaver flag_saver_;
@@ -191,6 +196,10 @@ TEST_F(UsageReportingTest, TestFlagsHelpHRF) {
       Some more help.
       Even more long long long long long long long long long long long long help
       message.); default: "";
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )";
 
   std::stringstream test_buf_01;
@@ -214,7 +223,11 @@ TEST_F(UsageReportingTest, TestFlagsHelpHRF) {
   EXPECT_EQ(test_buf_04.str(),
             R"(usage_test: Custom usage message
 
-  No modules matched: use -helpfull
+No flags matched.
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 
   std::stringstream test_buf_05;
@@ -226,12 +239,8 @@ TEST_F(UsageReportingTest, TestFlagsHelpHRF) {
       absl::StartsWith(test_out_str, "usage_test: Custom usage message"));
   EXPECT_TRUE(absl::StrContains(
       test_out_str, "Flags from absl/flags/internal/usage_test.cc:"));
-  EXPECT_TRUE(absl::StrContains(test_out_str,
-                                "Flags from absl/flags/internal/usage.cc:"));
   EXPECT_TRUE(
       absl::StrContains(test_out_str, "-usage_reporting_test_flag_01 "));
-  EXPECT_TRUE(absl::StrContains(test_out_str, "-help (show help"))
-      << test_out_str;
 }
 
 // --------------------------------------------------------------------
@@ -244,7 +253,40 @@ TEST_F(UsageReportingTest, TestNoUsageFlags) {
 // --------------------------------------------------------------------
 
 TEST_F(UsageReportingTest, TestUsageFlag_helpshort) {
-  absl::SetFlag(&FLAGS_helpshort, true);
+  flags::SetFlagsHelpMode(flags::HelpMode::kShort);
+
+  std::stringstream test_buf;
+  EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 1);
+  EXPECT_EQ(test_buf.str(),
+            R"(usage_test: Custom usage message
+
+  Flags from absl/flags/internal/usage_test.cc:
+    --usage_reporting_test_flag_01 (usage_reporting_test_flag_01 help message);
+      default: 101;
+    --usage_reporting_test_flag_02 (usage_reporting_test_flag_02 help message);
+      default: false;
+    --usage_reporting_test_flag_03 (usage_reporting_test_flag_03 help message);
+      default: 1.03;
+    --usage_reporting_test_flag_04 (usage_reporting_test_flag_04 help message);
+      default: 1000000000000004;
+    --usage_reporting_test_flag_05 (usage_reporting_test_flag_05 help message);
+      default: UDT{};
+    --usage_reporting_test_flag_06 (usage_reporting_test_flag_06 help message.
+
+      Some more help.
+      Even more long long long long long long long long long long long long help
+      message.); default: "";
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
+)");
+}
+
+// --------------------------------------------------------------------
+
+TEST_F(UsageReportingTest, TestUsageFlag_help_simple) {
+  flags::SetFlagsHelpMode(flags::HelpMode::kImportant);
 
   std::stringstream test_buf;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 1);
@@ -267,13 +309,42 @@ TEST_F(UsageReportingTest, TestUsageFlag_helpshort) {
       Some more help.
       Even more long long long long long long long long long long long long help
       message.); default: "";
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
+)");
+}
+
+// --------------------------------------------------------------------
+
+TEST_F(UsageReportingTest, TestUsageFlag_help_one_flag) {
+  flags::SetFlagsHelpMode(flags::HelpMode::kMatch);
+  flags::SetFlagsHelpMatchSubstr("usage_reporting_test_flag_06");
+
+  std::stringstream test_buf;
+  EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 1);
+  EXPECT_EQ(test_buf.str(),
+            R"(usage_test: Custom usage message
+
+  Flags from absl/flags/internal/usage_test.cc:
+    --usage_reporting_test_flag_06 (usage_reporting_test_flag_06 help message.
+
+      Some more help.
+      Even more long long long long long long long long long long long long help
+      message.); default: "";
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 }
 
 // --------------------------------------------------------------------
 
-TEST_F(UsageReportingTest, TestUsageFlag_help) {
-  absl::SetFlag(&FLAGS_help, true);
+TEST_F(UsageReportingTest, TestUsageFlag_help_multiple_flag) {
+  flags::SetFlagsHelpMode(flags::HelpMode::kMatch);
+  flags::SetFlagsHelpMatchSubstr("test_flag");
 
   std::stringstream test_buf;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 1);
@@ -297,14 +368,16 @@ TEST_F(UsageReportingTest, TestUsageFlag_help) {
       Even more long long long long long long long long long long long long help
       message.); default: "";
 
-Try --helpfull to get a list of all flags.
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 }
 
 // --------------------------------------------------------------------
 
 TEST_F(UsageReportingTest, TestUsageFlag_helppackage) {
-  absl::SetFlag(&FLAGS_helppackage, true);
+  flags::SetFlagsHelpMode(flags::HelpMode::kPackage);
 
   std::stringstream test_buf;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 1);
@@ -328,14 +401,16 @@ TEST_F(UsageReportingTest, TestUsageFlag_helppackage) {
       Even more long long long long long long long long long long long long help
       message.); default: "";
 
-Try --helpfull to get a list of all flags.
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 }
 
 // --------------------------------------------------------------------
 
 TEST_F(UsageReportingTest, TestUsageFlag_version) {
-  absl::SetFlag(&FLAGS_version, true);
+  flags::SetFlagsHelpMode(flags::HelpMode::kVersion);
 
   std::stringstream test_buf;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 0);
@@ -349,7 +424,7 @@ TEST_F(UsageReportingTest, TestUsageFlag_version) {
 // --------------------------------------------------------------------
 
 TEST_F(UsageReportingTest, TestUsageFlag_only_check_args) {
-  absl::SetFlag(&FLAGS_only_check_args, true);
+  flags::SetFlagsHelpMode(flags::HelpMode::kOnlyCheckArgs);
 
   std::stringstream test_buf;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf, kTestUsageMessage), 0);
@@ -359,17 +434,22 @@ TEST_F(UsageReportingTest, TestUsageFlag_only_check_args) {
 // --------------------------------------------------------------------
 
 TEST_F(UsageReportingTest, TestUsageFlag_helpon) {
-  absl::SetFlag(&FLAGS_helpon, "bla-bla");
+  flags::SetFlagsHelpMode(flags::HelpMode::kMatch);
+  flags::SetFlagsHelpMatchSubstr("/bla-bla.");
 
   std::stringstream test_buf_01;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf_01, kTestUsageMessage), 1);
   EXPECT_EQ(test_buf_01.str(),
             R"(usage_test: Custom usage message
 
-  No modules matched: use -helpfull
+No flags matched.
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 
-  absl::SetFlag(&FLAGS_helpon, "usage_test");
+  flags::SetFlagsHelpMatchSubstr("/usage_test.");
 
   std::stringstream test_buf_02;
   EXPECT_EQ(flags::HandleUsageFlags(test_buf_02, kTestUsageMessage), 1);
@@ -392,6 +472,10 @@ TEST_F(UsageReportingTest, TestUsageFlag_helpon) {
       Some more help.
       Even more long long long long long long long long long long long long help
       message.); default: "";
+
+Try --helpfull to get a list of all flags or --help=substring shows help for
+flags which include specified substring in either in the name, or description or
+path.
 )");
 }
 
diff --git a/absl/flags/parse.cc b/absl/flags/parse.cc
index 1835a837..dd1a6796 100644
--- a/absl/flags/parse.cc
+++ b/absl/flags/parse.cc
@@ -713,6 +713,11 @@ std::vector<char*> ParseCommandLineImpl(int argc, char* argv[],
     std::tie(flag, is_negative) = LocateFlag(flag_name);
 
     if (flag == nullptr) {
+      // Usage flags are not modeled as Abseil flags. Locate them separately.
+      if (flags_internal::DeduceUsageFlags(flag_name, value)) {
+        continue;
+      }
+
       if (on_undef_flag != OnUndefinedFlag::kIgnoreUndefined) {
         undefined_flag_names.emplace_back(arg_from_argv,
                                           std::string(flag_name));
diff --git a/absl/flags/parse_test.cc b/absl/flags/parse_test.cc
index d35a6e47..41bc0bc6 100644
--- a/absl/flags/parse_test.cc
+++ b/absl/flags/parse_test.cc
@@ -28,6 +28,7 @@
 #include "absl/flags/declare.h"
 #include "absl/flags/flag.h"
 #include "absl/flags/internal/parse.h"
+#include "absl/flags/internal/usage.h"
 #include "absl/flags/reflection.h"
 #include "absl/strings/str_cat.h"
 #include "absl/strings/string_view.h"
@@ -207,6 +208,9 @@ namespace flags = absl::flags_internal;
 using testing::ElementsAreArray;
 
 class ParseTest : public testing::Test {
+ public:
+  ~ParseTest() override { flags::SetFlagsHelpMode(flags::HelpMode::kNone); }
+
  private:
   absl::FlagSaver flag_saver_;
 };
@@ -851,7 +855,7 @@ TEST_F(ParseTest, TestIgnoreUndefinedFlags) {
 
 // --------------------------------------------------------------------
 
-TEST_F(ParseDeathTest, TestHelpFlagHandling) {
+TEST_F(ParseDeathTest, TestSimpleHelpFlagHandling) {
   const char* in_args1[] = {
       "testbin",
       "--help",
@@ -870,11 +874,38 @@ TEST_F(ParseDeathTest, TestHelpFlagHandling) {
       flags::UsageFlagsAction::kIgnoreUsage,
       flags::OnUndefinedFlag::kAbortIfUndefined);
 
+  EXPECT_EQ(flags::GetFlagsHelpMode(), flags::HelpMode::kImportant);
   EXPECT_EQ(absl::GetFlag(FLAGS_int_flag), 3);
 }
 
 // --------------------------------------------------------------------
 
+TEST_F(ParseDeathTest, TestSubstringHelpFlagHandling) {
+  const char* in_args1[] = {
+      "testbin",
+      "--help=abcd",
+  };
+
+  auto out_args1 = flags::ParseCommandLineImpl(
+      2, const_cast<char**>(in_args1), flags::ArgvListAction::kRemoveParsedArgs,
+      flags::UsageFlagsAction::kIgnoreUsage,
+      flags::OnUndefinedFlag::kAbortIfUndefined);
+
+  EXPECT_EQ(flags::GetFlagsHelpMode(), flags::HelpMode::kMatch);
+  EXPECT_EQ(flags::GetFlagsHelpMatchSubstr(), "abcd");
+
+  const char* in_args2[] = {"testbin", "--help", "some_positional_arg"};
+
+  auto out_args2 = flags::ParseCommandLineImpl(
+      3, const_cast<char**>(in_args2), flags::ArgvListAction::kRemoveParsedArgs,
+      flags::UsageFlagsAction::kIgnoreUsage,
+      flags::OnUndefinedFlag::kAbortIfUndefined);
+
+  EXPECT_EQ(flags::GetFlagsHelpMode(), flags::HelpMode::kImportant);
+}
+
+// --------------------------------------------------------------------
+
 TEST_F(ParseTest, WasPresentOnCommandLine) {
   const char* in_args1[] = {
       "testbin",        "arg1", "--bool_flag",
diff --git a/absl/flags/reflection_test.cc b/absl/flags/reflection_test.cc
index 8620d140..4c809009 100644
--- a/absl/flags/reflection_test.cc
+++ b/absl/flags/reflection_test.cc
@@ -32,8 +32,6 @@ ABSL_FLAG(int, int_flag, 1, "int_flag help");
 ABSL_FLAG(std::string, string_flag, "dflt", "string_flag help");
 ABSL_RETIRED_FLAG(bool, bool_retired_flag, false, "bool_retired_flag help");
 
-ABSL_DECLARE_FLAG(bool, help);
-
 namespace {
 
 namespace flags = absl::flags_internal;
@@ -66,12 +64,9 @@ TEST_F(ReflectionTest, TestFindCommandLineFlag) {
 // --------------------------------------------------------------------
 
 TEST_F(ReflectionTest, TestGetAllFlags) {
-  (void)absl::GetFlag(FLAGS_help);  // Force linking of usage flags.
-
   auto all_flags = absl::GetAllFlags();
   EXPECT_NE(all_flags.find("int_flag"), all_flags.end());
   EXPECT_EQ(all_flags.find("bool_retired_flag"), all_flags.end());
-  EXPECT_NE(all_flags.find("help"), all_flags.end());
   EXPECT_EQ(all_flags.find("some_undefined_flag"), all_flags.end());
 
   std::vector<absl::string_view> flag_names_first_attempt;
diff --git a/absl/status/internal/status_internal.h b/absl/status/internal/status_internal.h
index 1f82b8e4..279f8f55 100644
--- a/absl/status/internal/status_internal.h
+++ b/absl/status/internal/status_internal.h
@@ -36,6 +36,13 @@ using Payloads = absl::InlinedVector<Payload, 1>;
 
 // Reference-counted representation of Status data.
 struct StatusRep {
+  StatusRep(absl::StatusCode code, std::string message,
+            std::unique_ptr<status_internal::Payloads> payloads)
+      : ref(int32_t{1}),
+        code(code),
+        message(std::move(message)),
+        payloads(std::move(payloads)) {}
+
   std::atomic<int32_t> ref;
   absl::StatusCode code;
   std::string message;
diff --git a/absl/status/status.cc b/absl/status/status.cc
index a27fd8b3..c71de846 100644
--- a/absl/status/status.cc
+++ b/absl/status/status.cc
@@ -209,11 +209,8 @@ void Status::UnrefNonInlined(uintptr_t rep) {
 
 uintptr_t Status::NewRep(absl::StatusCode code, absl::string_view msg,
                          std::unique_ptr<status_internal::Payloads> payloads) {
-  status_internal::StatusRep* rep = new status_internal::StatusRep;
-  rep->ref.store(1, std::memory_order_relaxed);
-  rep->code = code;
-  rep->message.assign(msg.data(), msg.size());
-  rep->payloads = std::move(payloads);
+  status_internal::StatusRep* rep = new status_internal::StatusRep(
+      code, std::string(msg.data(), msg.size()), std::move(payloads));
   return PointerToRep(rep);
 }